Insulated clamping means



April 21, 1959 B. R. HERMANN INSULATED CLAMPING MEANS Filed Aug. 28, 1957 United States Patent INSULATED CLAMPING MEANS Benjamin R. Hermann, Pittsfield, Mass., assignor to General Electric Company, a corporation of New York Application August 28, 1957, Serial No. 680,844 1 Claim. (Cl. 174-163) This invention relates to insulated clamping means, and more particularly, to insulated clamping means such as straps, bands, U-bolts and the like for electrical insulators of the column type.

In circuit interrupters of the open type which use column insulators, the hardware such as the terminal contacts and hanger brackets have been connected thereto by generally U-shaped elements such as straps, bands, bolts or the like which have been clamped to the insulator. In order to bird proof these devices as well as to provide against flashover, it has been well known to electrically insulate these elements. One expedient has been to mold insulation about these elements. Another expedient has been to use a shield which is snapped over the elements. Neither of these solutions has proved to be successful.

In those situations where the elements have had insulation molded thereabout, the elements have become loose and the insulation has developed cracks and become generally deteriorated. In those situations where shields have been used, the shields have had conducting carbon tracks formed thereon.

I have discovered that the molded-in elements have become loose and their insulation cracked and generally deteriorated because of cold flow of the insulation. Also, the shields have developed carbon tracks because they have been placed in contact with these elements.

It is an object of this invention to provide an improved insulated clamping means which will overcome the above discussed disadvantages.

It is a further object of this invention to provide an improved generally U-shaped insulator clamping means for the column insulators of electrical circuit interrupters.

The features of my invention which I believe to be novel are set forth with particularity in the appended claim. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing; in which:

Fig. l is a partly broken away elevation view of one form of my invention; and

Fig. 2 is a sectional view taken along the line 22 of Fig. 1; and

Fig. 3 is a sectional view taken along the line 3-3 of Fig. 1.

Referring now particularly to Fig. 1 of the drawing, illustrated therein is a flip open fused circuit interrupter. The device comprises a column insulator 1 which has a pair of resilient arms 2 and 3 connected to the opposite ends thereof. The arm 2 is provided with a line terminal 4 and the arm 3 is provided with a line terminal 5. The arms 2 and 3 have contact portions 6 and 7 respectively formed at their outer ends. The contact portions 6 and 7 are adapted to have the opposite ends of a fuse assembly 8 wedged therein.

The device is adopted to be supported from the cross arm of a not shown line pole through the medium of a mounting bracket 9 which is connected to the central portion of the insulator 1 by a clamping band or strap 10. The upper arm 2 and its terminal 4 is clamped to the upper end of the insulator 1 by a generally U- shaped bolt 11. The lower arm 3 and its terminal 5 can be connected to the lower end of the insulator by appropriate means such as nuts and bolts. The insulator 1 may have a plurality of petticoats 12 formed thereon to provide the necessary electrical creepage distances between the spaced hardware.

The device may utilize a solid or a hollow electrical insulator. This form of electrical circuit interrupter is well known and may be used to protect electrical apparatus such as pole type transformers by connecting the terminal 5 to the transformer and the terminal 4 to the distribution line. If an overcurrent should occur in the protected apparatus, a fusible element in the fuse assembly 8 will melt which will permit the arms 2 and 3 to separate the opposite ends of the fuse element.

The upper and central clamping elements 11 and 10 respectively are generally U-shaped and they are reversed with respect to each other so that their bridge porfions are located on the left and right hand side respectively of the insulator 1. These bridge portions are reversed and electrically insulated in order to bird proof the device and provide long flashover and electrical creepage distances.

The element 11 is electrically insulated by intimately forming an electrical insulating material 13 thereabout. The electrical insulation 13 does not cover all of the curved or bridge portion of the element 11 but the inner circumference of the element 11 is exposed through the insulation. In this manner, the clamping forces are carried by the element 11 and are not transmitted to the insulation 13. The insulation can be formed on the member 11 by molding or casting methods. Also, the insulation can be sprayed thereon or the member 11 can be dipped in insulation after its inner circumference has been masked. If the inner circumference is not masked, then the insulation along the inner circumference can be scrapped or cut away to expose the inner circumference of the member 11. Methods such as casting, molding, spraying or dipping are used since by these methods the insulation is intimately formed on the member 11. That is, methods of this type avoid gaps, spaces or voids between the member 11 and the insulation. Many electrical insulating materials will be deformed or experience cold flow when highly compressed. By keeping the clamping forces off the insulation 13, it is not deformed, cracked, or otherwise damaged. Heretofore, the insulation 13 covered the inner circumference of the element 11 and it was disposed between the insulator 1 and the element 11. In such arrangement of the parts, the high clamping pressures were transmitted directly to the insulation. This deformed and cracked the insulation which made it ineffective as an electrical insulating material medium and eventually resulted in working loose of the upper clamping means. In the preferred form of the invention, all of the inner circumference of member 11 is exposed. However, it will be obvious that the clamping forces can be kept off the insulation by forming projections on the inner circumference which are exposed in which event the remaining portion of the inner circumference can be insulated.

The upper end of the insulator can have a small circumferential groove 14 which will seat the exposed inner circumferential edge of the U-shaped bolt 11. In this manner, the upper clamping means is retained in proper position.

The central clamping means 10 is electrically insulated by a curved electrical insulating material element 15.

Patented Apr. 21, 1959.

asssaas The element 15 can extend for slightly more than 180 about the insulator 1 so that it can be snapped on the insulator 1 and retained thereon without any special connecting means. The two petticoats which are immediately adjacent to the strap may have a small shoulder 16 formed thereon to help keep the shield properly located. Heretofore, a snap-on shield similar to element 15 was snapped directly about the central strap and placed in contact therewith. Such arrangement resulted in conducting carbon tracks on the shield which made it ineffective for its intended purposes. By spacing the shield 15 from the strap 10, carbon tracks on the shield 15 are substantially, if not entirely, eliminated.

The insulation 13 is made from an organic insulating material which is resistant to carbon tracking of the creepage type since it is in direct contact with conductive.

element 11. Examples of such materials and their ability to resist creepage tracking are disclosed in detail in copending Norman and Kessel patent application Serial No. 633,356 for Electrical Apparatus Insulation filed on January 9, 1957, and assigned to the same assignee as the instant case. Broadly, they consist of butyl gum or epoxy or polyester resin which have had critical amounts of hydrated alumina interspersed therein. Since insulation 15 is spaced from conductive element 10, it need not necessarily be made from organic insulating materials which are resistant to creepage trackmg.

In my invention, I prefer to use a spaced insulating shield such as 15 about the central clamping means inasmuch as it is considerably lower in cost than the upper insulated clamping means. Also, such a spaced snapon shield can be readily provided for the central straps of existing circuit interrupters without making any major changes in the circuit interrupter. The U-bolt 11 and its insulation 13 is preferred for the upper end of the insulator inasmuch as a shield such as 15 at the upper end of the insulator would necessitate an additional petticoat or the like at the upper end of the insulator. Since petticoats are already provided at the central part of the insulator, this is an additional reason for using the shield 15 about the central clamping means. However, it will be appreciated that either insulated clamping means can be used at either location if so desired.

While there have been shown and described particular embodiments of the invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention, and, therefore, it is intended by the appended claim to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

In a circuit interrupter which comprises a column insulator which has spaced hardware connected thereto, means for connecting said hardware to said insulator comprising a pair of generally U-shaped metallic elements which are clamped to said insulator in spaced and reversed relationship with respect to each other, and means for electrically insulating the bridge portions of each of said elements, one of said bridge portions having an electrical insulating material intimately formed thereabout except along the inner circumference thereof, and the other of said bridge portions being insulated by a generally U-shaped insulating material member which is connected to said insulator in spaced superposed relationship with respect to but without making contact with said other bridge portion, the metallic element of said one bridge portion being clamped to one end of said insulator, said one end having a circumferentially extending groove formed therein and the inner circumference of said one bridge portion being seated in said groove, the other metallic element being clamped to a central portion of said insulator, a plurality of circumferentially extending petticoats formed on said insulator between said two metallic elements and on opposite sides of said other metallic element, the two pettticoats immediately adjacent to the opposite sides of said other metallic element having shoulders formed thereon for seating said U-shaped insulating material member on said insulator in spaced relationship with respect to said other metallic element, and a terminal clamp connected to said end metallic element and a mounting strap connected to said other metallic element on opposite sides of said insulator.

References Cited in the file of this patent UNITED STATES PATENTS 1,903,784 King Apr. 18, 1933 2,065,315 Keath Dec. 22, 1936 2,269,610 Thompson Jan. 13, 1942 2,685,013 Strobel July 27, 1954 

